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rcu: Add tracing for RCU_FAST_NO_HZ 

This commit adds trace_rcu_prep_idle(), which is invoked from
rcu_prepare_for_idle() and rcu_wake_cpu() to trace attempts on
the part of RCU to force CPUs into dyntick-idle mode.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2011-11-22 14:58:03 -08:00 committed by Paul E. McKenney
parent 045fb9315a
commit 433cdddcd9
2 changed files with 52 additions and 3 deletions
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37
include/trace/events/rcu.h
View File

@ -274,6 +274,42 @@ TRACE_EVENT(rcu_dyntick,
__entry->oldnesting, __entry->newnesting)
);
/*
* Tracepoint for RCU preparation for idle, the goal being to get RCU
* processing done so that the current CPU can shut off its scheduling
* clock and enter dyntick-idle mode. One way to accomplish this is
* to drain all RCU callbacks from this CPU, and the other is to have
* done everything RCU requires for the current grace period. In this
* latter case, the CPU will be awakened at the end of the current grace
* period in order to process the remainder of its callbacks.
*
* These tracepoints take a string as argument:
*
* "No callbacks": Nothing to do, no callbacks on this CPU.
* "In holdoff": Nothing to do, holding off after unsuccessful attempt.
* "Dyntick with callbacks": Callbacks remain, but RCU doesn't need CPU.
* "Begin holdoff": Attempt failed, don't retry until next jiffy.
* "More callbacks": Still more callbacks, try again to clear them out.
* "Callbacks drained": All callbacks processed, off to dyntick idle!
* "CPU awakened at GP end":
*/
TRACE_EVENT(rcu_prep_idle,
TP_PROTO(char *reason),
TP_ARGS(reason),
TP_STRUCT__entry(
__field(char *, reason)
),
TP_fast_assign(
__entry->reason = reason;
),
TP_printk("%s", __entry->reason)
);
/*
* Tracepoint for the registration of a single RCU callback function.
* The first argument is the type of RCU, the second argument is
@ -482,6 +518,7 @@ TRACE_EVENT(rcu_torture_read,
#define trace_rcu_quiescent_state_report(rcuname, gpnum, mask, qsmask, level, grplo, grphi, gp_tasks) do { } while (0)
#define trace_rcu_fqs(rcuname, gpnum, cpu, qsevent) do { } while (0)
#define trace_rcu_dyntick(polarity, oldnesting, newnesting) do { } while (0)
#define trace_rcu_prep_idle(reason) do { } while (0)
#define trace_rcu_callback(rcuname, rhp, qlen) do { } while (0)
#define trace_rcu_kfree_callback(rcuname, rhp, offset, qlen) do { } while (0)
#define trace_rcu_batch_start(rcuname, qlen, blimit) do { } while (0)

18
kernel/rcutree_plugin.h
View File

@ -2031,10 +2031,13 @@ static void rcu_prepare_for_idle(int cpu)
/* If no callbacks or in the holdoff period, enter dyntick-idle. */
if (!rcu_cpu_has_callbacks(cpu)) {
per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
trace_rcu_prep_idle("No callbacks");
return;
}
if (per_cpu(rcu_dyntick_holdoff, cpu) == jiffies)
if (per_cpu(rcu_dyntick_holdoff, cpu) == jiffies) {
trace_rcu_prep_idle("In holdoff");
return;
}
/* Check and update the rcu_dyntick_drain sequencing. */
if (per_cpu(rcu_dyntick_drain, cpu) <= 0) {
@ -2044,9 +2047,11 @@ static void rcu_prepare_for_idle(int cpu)
/* We have hit the limit, so time to give up. */
per_cpu(rcu_dyntick_holdoff, cpu) = jiffies;
if (!rcu_pending(cpu)) {
trace_rcu_prep_idle("Dyntick with callbacks");
per_cpu(rcu_awake_at_gp_end, cpu) = 1;
return; /* Nothing to do immediately. */
}
trace_rcu_prep_idle("Begin holdoff");
invoke_rcu_core(); /* Force the CPU out of dyntick-idle. */
return;
}
@ -2073,9 +2078,15 @@ static void rcu_prepare_for_idle(int cpu)
c = c || per_cpu(rcu_bh_data, cpu).nxtlist;
}
/* If RCU callbacks are still pending, RCU still needs this CPU. */
if (c)
/*
* If RCU callbacks are still pending, RCU still needs this CPU.
* So try forcing the callbacks through the grace period.
*/
if (c) {
trace_rcu_prep_idle("More callbacks");
invoke_rcu_core();
} else
trace_rcu_prep_idle("Callbacks drained");
}
/*
@ -2085,6 +2096,7 @@ static void rcu_prepare_for_idle(int cpu)
*/
static void rcu_wake_cpu(void *unused)
{
trace_rcu_prep_idle("CPU awakened at GP end");
invoke_rcu_core();
}